That's a nice one! I just dug a 1921 in near unworn condition (F-12 condition, actually) about a month or two ago. I knew right away I had some money in my hand, because a few years later the coin was re-designed so they wouldn't wear so fast. I needed some fast money so I sold it to a local dealer who is more fair than others around here. He gave me $150 for it, which I think is fair since the guy has to pay rent and all that. My coin book is older and it had it at I think $250 or so maybe from memory. Later I figured out how you can check how much items sold for on Ebay where the bidding has ended and found my year, my shape...was being sold at around $350 to $450. Oh well, my fault for not using a newer coin book, and next time I know how to check Ebay to see how much stuff has sold for. I'm still happy with the $150 because I really needed the cash that week for some issues, and besides I was always told to never look a gift horse in the mouth.
Far as I'm concerned coins are nice to keep in a collection, but a good picture is all I really care to have for the most part to remember it by. Sure, I hang onto all my copper coins and such since most aren't worth anything, but silver is always paying a high X face value even if it's a common date, so when I get enough of a pile going I cash it in. Down the road when money ain't as tight I'll hang onto my silver too. Usually I have a nice pile I intend to keep, but then something comes up and I end up cashing all the common dates in for the X times face value amount.
I just can't understand why that coin is that shiny though. I shine my common date silver because I think it's stupid not to have silver look pristine IMO, but the stuff that has some value other than face value...only water and soap. If you used just water and soap then no reason they can even tell it's been cleaned. Just don't tell them you dug it out of the ground because then they'll know you washed it off. Don't even mention you washed it with soap and water, because far as I know there is no way to tell that's been done and I thought was an acceptable practice without degrading the coin's value? For my common date stuff I rub the coin between my fingers with a little baking soda and water and it shines them right up. If they have some really stubborn black stains that that won't take off for some reason, then I use electrolysis on them and it will bust anything off them real quick. A great way to clean silver rings too that have nooks and crannies you can't reach.
PS- I have to agree that I've never dug a coin that shiney. They always have at least a few darker or stain spots on them. You sure you only used dishwashing soap and water with a non-abbrassive towel? And was the soap non-abbrassive?